1. Field of the Invention
The present invention relates generally to interrupter devices for high voltage AC distribution systems, and more particularly, to an interrupter assembly comprising an interrupter switch and a condition sensing device, wherein the interrupter assembly and condition sensing device are each embedded in a solid dielectric material.
2. Description of the Prior Art
Vacuum interrupters or switches are employed in many high voltage applications to perform various interrupting and switching functions. For example, vacuum interrupters are used in reclosers, circuit breakers, intelligent switches for automated power distribution, and indoor switchgear. A typical vacuum interrupter comprises a pair of large-surface electrical contacts arranged in an axial configuration and enclosed within an evacuated metal-ceramic housing. One of the contacts is stationary, while the other moves in an axial direction to open and close the contacts.
In many applications, a number of vacuum interrupters are housed in a single enclosure along with related circuit components. For example, current and/or voltage sensors may be included to provide input to overcurrent protective relays, measuring devices and monitoring relay schemes in the control function of the equipment. Typically, the enclosures are filled with an insulating oil or gas (e.g. SF.sub.6) having a high dielectric strength to provide electrical insulation between the vacuum interrupters and other components. Immersing the interrupters and associated sensing devices in an insulating oil or gas allows the individual assemblies to be mounted in closer proximity, thus reducing the overall size and cost of the equipment. In some cases, however, the current and voltage sensing devices are mounted separately from the vacuum interrupters to further isolate these components. Unfortunately, use of insulating oils or gases makes maintenance of the equipment more difficult and often requires special handling equipment. Additionally, there is a growing environmental concern with respect to a number of oil and gas compositions currently employed in the high voltage equipment industry.
Recently, the electrical utility industry has been exploring the use of polymer concrete and similar dielectric materials as a replacement for porcelain in a wide variety of insulating applications. Polymer concretes are composite materials consisting of inorganic aggregates, such as silica, bonded together with a low viscosity organic resin. The most widely known polymer concrete formulations have been trademarked by the Electric Power Research Institute under the trade name Polysil. Polymer concretes are mechanically strong and have excellent electrical properties, including a Dielectric Strength in the range of 400 V/mil. Additionally, polymer concretes can be easily molded or cast into complex shapes. Epoxy-concrete is a similar solid dielectric material wherein epoxy is used to bond the silica aggregates. Various epoxy resins which do not contain silica aggregates, such as cycloaliphatic epoxy resin, also provide similar properties.
Nonken, U.S. Pat. No. 3,812,314, discloses an interrupter assembly for use in underground electric power distribution systems that comprises a vacuum interrupter switch embedded in a bushing formed of electrically insulated epoxy resin. However, Nonken does not teach or suggest encapsulating other devices, such as current or voltage sensors, within the bushing to create a single multi-function assembly.
Reighter, U.S. Pat. No. 4,267,402, discloses an insulator formed of polymer concrete that has mounting threads molded directly into the polymer concrete. St-Jean et al., U.S. Pat. No. 4,827,370 discloses a cylindrical enclosure formed of epoxy-concrete or polymeric concrete for housing a surge arrester. Lindsey, U.S. Pat. No. 4,823,022, discloses a power line insulator formed of Polysil. A voltage sensor, current sensor and terminal box are embedded in the Polysil during the molding process for the insulator.
Although Nonken teaches embedding a vacuum interrupter in an epoxy resin and Lindsey teaches embedding voltage and current sensing devices in a power line insulator formed of Polysil, the prior art has not recognized the reduced size, ease of maintenance and environmental advantages of combining a vacuum interrupter and current/voltage sensing devices in a single cast/molded interrupter assembly formed of polymer concrete or a similar solid dielectric material. Such assemblies would eliminate the need for an insulating oil or gas and would allow reduced spacing between adjacent interrupter assemblies in a wide variety of high voltage equipment. By incorporating a current and/or voltage sensing device in the solid dielectric material, the need to mount these devices separately or provide additional insulation would be eliminated.